The April 2017 Mw6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

International audienceLarge earthquakes in stable continental regions remain puzzling as; unlike at plate boundaries, they do not result from the local buildup of strain driven by plate tectonics. The 2017 Mw6.5, Bostwana normal faulting earthquake occurred in a region devoid from recent tectonic activity and where present-day deformation is negligible. The depth of the event (29 ± 4 km), in a felsic lower crust where ductile deformation is expected, likely requires a transient pulse of fluids from a deep source to activate brittle faulting. The mainshock was preceded by two foreshock swarm-like sequences that may be further evidence for fluid movement in a critically loaded fault network. Contrary to plate boundary events, the Mw6.5 Botswana earthquake did not require prior localized stress or strain accumulation. We propose that the crust in stable continental regions, even long after the last tectonic episode, constitutes a reservoir of elastic stress that can be released episodically, for instance, as a result of deep fluid migration